dt-bindings: display: tegra: vi: add 'vip' property and example

The Tegra20 VI peripheral can receive parallel input from the VIP parallel
input module. Add it to the allowed properties and augment the existing
nvidia,tegra20-vi example to show a 'vip' property.

Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>